The organization warns the decline of traditional apple orchards, where the parasitic plant thrives, threatens the yuletide tradition.
It says that in the apple-growing heartland of Somerset, Gloucestershire, Herefordshire and Worcestershire, orchards have declined dramatically over the past 60 years.
Besides bedecking the halls in December, mistletoe also provides an important winter food for birds and supports six insects, including the rare mistletoe marble moth.
Leading mistletoe expert Jonathan Briggs told The Guardian that people should make sure their mistletoe comes from sustainable sources in Britain.
That’s because the parasite can hasten the death of mature trees, and harvesting each holiday season keeps its growth in check.
Mistletoe bears fruit at the time of the Winter Solstice, the birth of the pagan new year, and may have been used in solstitial rites in Druidic Britain as a symbol of immortality.
In Celtic mythology and in Druid rituals, it was considered a remedy for barrenness in animals and an antidote to poison. But the fruits of many mistletoes contain viscotoxins and are actually poisonous if ingested.